1. Field of the Invention
This invention relates generally to iron containing, high redox ratio soda-lime-silica glasses and methods of making same, and more particularly, to low iron, high redox ratio, and high iron, high redox ratio, soda-lime-silica glasses, and methods of making same.
2. Discussion of Available Technology
As is appreciated by those skilled in the art of making soda-lime-silica glass, parameters of interest include, but are not limited to the redox ratio, and total iron expressed as Fe2O3. For example and not limiting to the discussion, U.S. Pat. No. 6,962,887, which patent is incorporated herein by reference, discloses a glass having total iron expressed as Fe2O3 in the range of greater than 0 to 0.02 weight percent (“wt. %”) and a redox ratio in the range of 0.2 to 0.6. The glass is aesthetically pleasing and useful, for example, in furniture applications such as tabletops or shelving. Further, this glass is highly transparent when viewed normal to a major surface of the glass but has an aesthetically desirable blue i.e., azure edge color when viewed on edge. Such a glass is sold by PPG Industries, Inc. under the PPG Industries Ohio registered trademark “Starphire”.
Another glass of interest in the present discussion is disclosed in U.S. Pat. No. 6,313,053, which patent is incorporated herein by reference. The patent discloses a blue colored glass using a standard soda-lime-silica glass base composition and additionally iron and cobalt, and optionally chromium, as solar radiation absorbing materials and colorants. The blue colored glass has total iron expressed as Fe2O3 in the range of 0.10 to 1.0 wt. %, and a redox ratio in the range of greater than 0.35 to 0.60. Such a glass is considered for purposes of discussion a high iron, high redox ratio, soda-lime-silica glass. Such a glass is sold by PPG Industries, Inc. under the PPG Industries Ohio registered trademark “Solextra”.
The low iron, and high Iron, high redox soda-lime-silica glass compositions can be made in a multi-stage melting and vacuum-assisted refining operation as disclosed in U.S. Pat. Nos. 4,792,536 and 5,030,594, and can be made in a conventional float glass system as disclosed in U.S. Pat. No. 6,962,887. U.S. Pat. Nos. 4,792,536, 5,030,594 and 6,962,887 are hereby Incorporated by reference. The high iron. and low iron, high redox ratio soda-lime-silica glass compositions am generally made in a conventional float glass system using oxyfuel as disclosed in U.S. Pat. Nos. 4,604,123; 6,962,887 and 7,691,763 to obtain or maintain a high redox ratio, and the low iron, high redox glasses can be made using oxyfuel fired furnaces but are preferably made using fuel and air mixtures fired In Siemens type furnaces. U.S. Pat. Nos. 4,604,123; 6,962,887 and 7,691,763 are hereby incorporated by reference. Although the presently available methods for making the glasses disclosed in U.S. Pat. Nos. 4,792,536, 5,030,594, 6,313,053 and 6,962,887 am acceptable; there are limitations. More particularly, the limitations of interest in the present discussion are maintaining the redox ratio of the glasses within a range of 0.2 to 0.6 and preferably within the range of 0.35 to 0.6.
As is appreciated by those skilled in the art, the redox ratio can be increased by additions of sulfur (see incorporated U.S. patents) and carbon, e.g. but not limited to graphite, coal and/or oil to reduce the Ferric iron (Fe+++) to Ferrous iron (Fe++). Although presently there are available methods for making glasses having low iron, high redox ratio, and high iron, high redox ratios, it is appreciated by those skilled in the art that the methods are usually tailored to meet the parameters of the furnace. More particularly, the use of carbon to increase the redox ratio of soda-lime-silica glasses made using oxyfuel fired glassmaking furnaces can result in batch melting changes that can result in silica stones. In view of the forgoing, it would be advantageous to provide methods for making low iron and high iron soda-lime-silica glasses having high redox ratios that can be used regardless of the type of heating system or furnace used to melt the glass batch materials and to eliminate the limitations associated with the heating systems.